summaryrefslogtreecommitdiff
diff options
context:
space:
mode:
-rw-r--r--Documentation/technical/index-format.txt94
1 files changed, 57 insertions, 37 deletions
diff --git a/Documentation/technical/index-format.txt b/Documentation/technical/index-format.txt
index 89e410a..7b233ca 100644
--- a/Documentation/technical/index-format.txt
+++ b/Documentation/technical/index-format.txt
@@ -9,21 +9,21 @@ GIT index format
- A 12-byte header consisting of
4-byte signature:
- The signature is { 'D', 'I', 'R', 'C' }
+ The signature is { 'D', 'I', 'R', 'C' } (stands for "dircache")
4-byte version number:
The current supported versions are 2 and 3.
32-bit number of index entries.
- - A number of sorted index entries
+ - A number of sorted index entries (see below).
- Extensions
Extensions are identified by signature. Optional extensions can
be ignored if GIT does not understand them.
- GIT currently supports tree cache and resolve undo extensions.
+ GIT currently supports cached tree and resolve undo extensions.
4-byte extension signature. If the first byte is 'A'..'Z' the
extension is optional and can be ignored.
@@ -38,8 +38,9 @@ GIT index format
== Index entry
Index entries are sorted in ascending order on the name field,
- interpreted as a string of unsigned bytes. Entries with the same
- name are sorted by their stage field.
+ interpreted as a string of unsigned bytes (i.e. memcmp() order, no
+ localization, no special casing of directory separator '/'). Entries
+ with the same name are sorted by their stage field.
32-bit ctime seconds, the last time a file's metadata changed
this is stat(2) data
@@ -62,12 +63,13 @@ GIT index format
32-bit mode, split into (high to low bits)
4-bit object type
- valid values in binary are 1000 (blob), 1010 (symbolic link)
+ valid values in binary are 1000 (regular file), 1010 (symbolic link)
and 1110 (gitlink)
3-bit unused
- 9-bit unix permission (only 0755 and 0644 are valid)
+ 9-bit unix permission. Only 0755 and 0644 are valid for regular files.
+ Symbolic links and gitlinks have value 0 in this field.
32-bit uid
this is stat(2) data
@@ -76,11 +78,11 @@ GIT index format
this is stat(2) data
32-bit file size
- This is the on-disk size from stat(2)
+ This is the on-disk size from stat(2), truncated to 32-bit.
160-bit SHA-1 for the represented object
- A 16-bit field split into (high to low bits)
+ A 16-bit 'flags' field split into (high to low bits)
1-bit assume-valid flag
@@ -88,7 +90,8 @@ GIT index format
2-bit stage (during merge)
- 12-bit name length if the length is less than 0x0FFF
+ 12-bit name length if the length is less than 0xFFF; otherwise 0xFFF
+ is stored in this field.
(Version 3) A 16-bit field, only applicable if the "extended flag"
above is 1, split into (high to low bits).
@@ -103,63 +106,80 @@ GIT index format
Entry path name (variable length) relative to top level directory
(without leading slash). '/' is used as path separator. The special
- paths ".", ".." and ".git" (without quotes) are disallowed.
+ path components ".", ".." and ".git" (without quotes) are disallowed.
Trailing slash is also disallowed.
The exact encoding is undefined, but the '.' and '/' characters
- are encoded in 7-bit ASCII and the encoding cannot contain a nul
- byte. Generally a superset of ASCII.
+ are encoded in 7-bit ASCII and the encoding cannot contain a NUL
+ byte (iow, this is a UNIX pathname).
1-8 nul bytes as necessary to pad the entry to a multiple of eight bytes
while keeping the name NUL-terminated.
== Extensions
-=== Tree cache
+=== Cached tree
- Tree cache extension contains pre-computed hashes for trees that can
+ Cached tree extension contains pre-computed hashes for trees that can
be derived from the index. It helps speed up tree object generation
from index for a new commit.
When a path is updated in index, the path must be invalidated and
removed from tree cache.
- - Extension tag { 'T', 'R', 'E', 'E' }
+ The signature for this extension is { 'T', 'R', 'E', 'E' }.
- - 32-bit size
+ A series of entries fill the entire extension; each of which
+ consists of:
- - A number of entries
+ - NUL-terminated path component (relative to its parent directory);
- NUL-terminated tree name
+ - ASCII decimal number of entries in the index that is covered by the
+ tree this entry represents (entry_count);
- Blank-terminated ASCII decimal number of entries in this tree
+ - A space (ASCII 32);
- Newline-terminated position of this tree in the parent tree. 0 for
- the root tree
+ - ASCII decimal number that represents the number of subtrees this
+ tree has;
- 160-bit SHA-1 for this tree and it's children
+ - A newline (ASCII 10); and
+
+ - 160-bit object name for the object that would result from writing
+ this span of index as a tree.
+
+ An entry can be in an invalidated state and is represented by having -1
+ in the entry_count field.
+
+ The entries are written out in the top-down, depth-first order. The
+ first entry represents the root level of the repository, followed by the
+ first subtree---let's call this A---of the root level (with its name
+ relative to the root level), followed by the first subtree of A (with
+ its name relative to A), ...
=== Resolve undo
- A conflict is represented in index as a set of higher stage entries.
+ A conflict is represented in the index as a set of higher stage entries.
When a conflict is resolved (e.g. with "git add path"), these higher
- stage entries will be removed and a stage-0 entry with proper
- resoluton is added.
+ stage entries will be removed and a stage-0 entry with proper resoluton
+ is added.
- Resolve undo extension saves these higher stage entries so that
- conflicts can be recreated (e.g. with "git checkout -m"), in case
- users want to redo a conflict resolution from scratch.
+ When these higher stage entries are removed, they are saved in the
+ resolve undo extension, so that conflicts can be recreated (e.g. with
+ "git checkout -m"), in case users want to redo a conflict resolution
+ from scratch.
- - Extension tag { 'R', 'E', 'U', 'C' }
+ The signature for this extension is { 'R', 'E', 'U', 'C' }.
- - 32-bit size
+ A series of entries fill the entire extension; each of which
+ consists of:
- - A number of conflict entries
+ - NUL-terminated pathname the entry describes (relative to the root of
+ the repository, i.e. full pathname);
- NUL-terminated conflict path
+ - Three NUL-terminated ASCII octal numbers, entry mode of entries in
+ stage 1 to 3 (a missing stage is represented by "0" in this field);
+ and
- Three NUL-terminated ASCII octal numbers, entry mode of entries in
- stage 1 to 3.
+ - At most three 160-bit object names of the entry in stages from 1 to 3
+ (nothing is written for a missing stage).
- At most three 160-bit SHA-1s of the entry in three stages from 1
- to 3. SHA-1 is not saved for any stage with entry mode zero.